Device for mixing two pasty materials, especially for mixing a dental impression material with a catalyst material

ABSTRACT

A device for mixing two pasty substances is provided with a housing including an essentially tubular section having two radial inlet openings at a rear end and an outlet opening at a front end of the tubular section, and a driveable mixer shaft extending through the tubular section and rotatably supported in the housing. The mixer shaft includes multiple rigid mixer elements protruding from an axis for mixing the two pasty substances when they pass through the tubular section. The mixer shaft includes at the level of the inlet openings at least one deflection element for promoting the axial transportation of the two pasty substances when fed through the inlet openings, wherein the at least one deflection element has a deflection surface extending about the axis and at an inclination to a radial plane of the axis.

BACKGROUND OF THE INVENTION

The invention relates to a device for mixing two pasty substances whichare in particular a dental impression substance and a catalyst substancefor accelerating polymerization of the dental impression substance.

The device according to the invention is attached onto the two outletstubs of a discharge device, via which the pasty substances are fed tothe mixing device by application of pressure, and after mixing in themixing device the pasty substances are discharged in the form of amixture.

In several technical applications it is necessary to apply twoseparately stored pasty substances in form of a mixture. For thispurpose either dynamical or statical continuous mixers are used whichmix the substances with each other when the pasty substances flowthrough a mixer housing. A dynamical mixer is known from EP-A-0 492 412.This known device comprises an essentially tubular mixer housing with amixer shaft rotatably arranged therein. The mixer shaft comprises aplurality of radially protruding web-shaped mixer elements which, whenthe mixer shaft is driven, serve for deflection of the substance flowsthus mixing the two pasty substances with each other. The pastysubstances are fed via a radial front wall at the rear end of the mixerhousing into the latter. For this purpose the front wall comprises twoinlet stubs which are attached onto the outlet stubs of a device fordischarging the pasty substances.

To prevent contamination in the direction of the outlet stubs of thedischarge device the known mixer comprises stripping elements protrudingfrom the mixer shaft, the stripping elements moving along the inner sideof the rear-side front wall and transporting pasty material entering viathe inlet stubs to the side. The pasty material supplied via one of theinlet stubs inside the housing is at least partially transported incircumferential direction by said strippers thus being fed to the areaof the other inlet stub where contamination in the direction of theinlet stub and further in the direction of the outlet stub of therespective discharge device connected with the inlet stub may occur whenthe dynamic mixer is not driven.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a device for mixing twopasty substances where the risk of contamination in backward directionis reduced.

To solve this object the invention suggests a device for mixing twopasty substances, the device comprising

a housing comprising an essentially tubular section having two radialinlet openings for the two pasty substances at the rear end and anoutlet opening for the mixed pasty substances at the front end of thetubular section,

a driveable mixer shaft extending through the tubular section androtatably supported in the housing,

wherein the mixer shaft comprises a plurality of rigid mixer elementsprotruding from an axis, the mixer elements serving for mixing the twopasty substances during their passage through the tubular section of thehousing.

According to the invention said device is characterized in that themixer shaft comprises at the level of the inlet openings at least onedeflection element for promoting the transport in axial direction of thepasty substances fed through the inlet openings to the tubular sectionof the housing, wherein the at least one deflection element comprises adeflection surface extending about the axis and at an inclination to aradial plane of the axis.

In the mixing device according to the invention (hereinafter referred toas dynamic mixer) the pasty substances to be mixed are radially suppliedto the essentially tubular section of the mixer housing. For thispurpose the tubular section of the housing is provided with two radialinlet openings in particular arranged diametrically opposite each other.The pasty substance flows fed to the mixer by application of pressureare supplied within the tubular section of the housing to at least onedeflection element which extends about the axis of the mixer shaft. Saiddeflection element rotates together with the rotating mixer shaft andcomprises a deflection surface extending at an inclination to a radialplane of the axis. In other words, the at least one deflection elementis an essentially saw-tooth wedge extending in an arcuate manner aboutthe axis of the mixer shaft. Said deflection element acts in the sameway as a screw conveyor in a screw-type pump and ensures that theincoming pasty material is directly transported in axial direction fromthe inlet openings towards the outlet opening. This reliably preventscontamination in backward direction since the at least one deflectionelement always promotes the axial transport of the pasty substances fedthrough the inlet openings to the tubular section of the mixer housing.

As already said above, the deflection element can be of wedge-typeconfiguration. Alternatively to this wedge form the deflection elementcan be designed as a web extending helically about the axis; in thisembodiment the deflection element is configured as a thread. Suchhelical webs are known from screw-type pumps and screw conveyors.

Advantageously, at the level of the radial inlet openings of the tubularsection of the housing two deflection elements are provided on the axis,the deflection elements appropriately being arranged diametricallyopposite each other. Said deflection elements or each deflection elementpreferably extends over an angular range of 180° to 90°.

To be able to attach the dynamic mixer according to the invention ontothe two outlet stubs of a squeezing device, the housing comprises at itsrear end an insertion part oriented at an inclination to the axis, onwhich insertion part two inlet stubs are protrudingly arranged. Saidinsertion part is located in a flared housing section of the mixerjoining the tubular section, and comprises two ducts extending from theinlet stub. Said two ducts radially extend, at an angle, to a centralcylindrical deepened reception portion on the inner side of theinsertion part, which deepened portion receives the axis of the mixershaft with the at least one deflection element. Thus the cylindricaldeepened reception portion of the insertion part forms a portion of thetubular housing section of the mixer.

According to a preferred aspect of the invention a plurality of mixerelements are located between the radial inlet openings and the axialoutlet opening within the tubular housing section, said mixer elementsprotruding in the form of radial webs from the axis and extending up tonear the inner surfaces of the tubular housing section. Within severalradial planes said mixer elements are arranged such that they protrudefrom the shaft, which results in deflection of substance flows axiallyextending through the housing. This leads to the desired mixing effect.The mixing effect is intensified when said mixer elements, which preventdirect flow between the inlet openings and the outlet opening due totheir radial orientation, extend over a larger angular range, e.g. 90°.This can be realized by connecting adjacent mixer elements via acircumferential portion. In this way, mixer elements in the form ofquarter circles are configured, wherein it may be of advantage if themiddle sections of these quarter circles, as seen in circumferentialdirection, protrude from the inner surface of the tubular section of thehousing to a larger extent than their ends. It is appropriate if twoadjacent radially extending mixer elements staggered from radial planeto radial plane, as seen in circumferential direction, are connectedwith each other in the manner described above.

Besides arrangement of the rigid mixer elements as described above it isof advantage with regard to the mixing process if the mixer shaftcomprises additional flexible stripper elements which move along theinner wall of the tubular housing due to their flexible configuration orat least due their flexible free ends arranged at a distance to theaxis. Hereunder an embodiment of the invention is explained in detailwith reference to the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general side view of a discharge device for mixed pastycomponents,

FIG. 2 shows a longitudinal section of the dynamic mixer used for thedischarge device shown in FIG. 1,

FIGS. 3 to 6 show cross-sections of the mixer shown in FIG. 2 along thelines III—III, IV—IV, V—V and VI—VI, and

FIG. 7 shows a cross-section similar to that of FIG. 6 but of analternative embodiment of the mixer shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a side view of a discharge device 10 for two pastycomponents to be mixed with each other. Said device 10 comprises asqueezing part 12 and a mixing part 14, said squeezing part 12 havingtwo pressure containers 16, 18 for receiving two bags 20,22 containingthe pasty substances. At the front ends 24,26 of the pressure containers16,18 the latter comprise outlet stubs 28,30 via which the contents ofthe bags 20,22 is discharged when pressure is applied to the rear end ofthe bags 20,22. Pressure is applied to the bags 20,22 by means ofmotor-driven pressure stamps 32,34, which is not shown in detail here.

Onto the outlet stubs 28,30 a dynamic mixer 36 is attached which ishereunder described in detail with reference to FIGS. 2 to 7. Concerningsaid dynamic mixer 36 it can generally be said that its mixer shaft 38is driven by a motor. For this purpose the mixer shaft 38 is adapted tobe coupled with a drive rod 40 which is rotatingly driven by a motorwhich is not shown either.

The details of the dynamic mixer 36 are shown in FIG. 2. This figureshows a longitudinal section of the mixer 36. The mixer 36 comprises ahousing 42 which has an essentially cylindrical or tubular section 44with a flared end section 46 at the rear end 48 facing the squeezingpart 12, and a tapered front end 50. Said tapered end 50 is designed asoutlet stub and defines the outlet opening 52 for the material mixture,while at the rear end 48 of the housing 42 two inlet stubs 54,56 arearranged which are adapted to be attached onto the outlet stubs 28,30 ofthe squeezing part 12. Between the two inlet stubs 54,56 a passage 58 isprovided in which one end 60 of the mixer shaft 38 is rotatablysupported. Via said passage the drive rod 40 can be coupled with themixer shaft 38.

The inlet stubs 54,56 and the passage 58 are configured in an insertionpart 62 which is inserted into the flared section 46 at the rear end 48of the housing 42. Proceeding from the inlet stubs 54,56 two ducts 64,66extend through the insertion part 62, the ducts being deflected andending in radial openings 68,70. Said inlet openings 68,70 are radiallyarranged relatively to the cylindrical section 44 of the mixer housing42. Via the ducts 64,66 the two pasty components are transported intothe dynamic mixer 36 where they are fed in radial direction to the mixershaft 38.

As can be seen in FIGS. 2 and 3 the insertion part 62 comprises acentral essentially cylindrical deepened reception portion 69 which isarranged concentrically to the passage 58 and into which the mixer shaft38 is inserted. In the cylindrical wall 71 of the deepened receptionportion 69 the inlet openings 68,70 are provided. Further, the ducts64,66 are configured in this area. Said ducts 64,66 are configured asgrooves or recesses which are open at the top and which, together withthe essentially flared housing section 46, form the ducts closed on allsides.

The mixer shaft 38 comprises a rotatably supported axis 72 from which,in a plurality of radial planes, four web-type mixer elements 74 eachprotrude essentially in radial direction. The exact arrangement of saidmixer elements 74 is shown in the sectional representation of FIG. 4. Itcan be seen that the mixer element 74 limiting side edges lying in thecircumferential direction extend essentially tangentially to thecircumferential surface of the axis 72. According to FIG. 4 four mixerelements 74 are provided for each radial plane, the mixer elements 74reaching up to near the inner surface 76 of the cylindrical housingsection 44 as is shown in FIG. 2. The overall area between the inletopenings 68,70 and the end of the mixer shaft 38, which extends up tothe tapered end 50 of the mixer housing 42, is provided with said mixerelements 74. Further, the mixer shaft 38 comprises mixer elements 78configured as quarter circuit areas which are formed by connecting twoadjacent mixer elements 74 of a radial plane (see, for example, thesectional representation of FIG. 5). In this embodiment the radiallyouter limiting edge of the mixer element 78 is of circular arcconfiguration, while it extends secantially in the alternative shown inFIG. 7. The mixer element 78′ shown in FIG. 7 thus comprises, in amiddle circumferential section, a larger section towards the innersurface 76 of the cylindrical housing section 44.

While the mixer elements 74,78,78′, owing to their radial extension upto near the cylindrical housing section 44, ensure deflection and thusswirling of the axially flowing pasty substances when the mixer shaft 38rotates, the mixer shaft 38 comprises in the area of the radial inletopenings 68,70 two deflection elements 80 configured in the form of ascrew conveyor. The deflection elements 80 are designed as saw-toothwedges extending over approximately 90° about the axis 72 of the mixershaft 38. Said deflection elements 80 have a deflection surface 82ascending in circumferential direction, said deflection surface 82 beingdirected towards the outlet end 52 of the dynamic mixer 36 and extendingat an angle to a plane extending radially to the axis 72. Saiddeflection elements 80 thus extend helically in sections and provide anaxial movement component of the pasty substance flows. Thus thedeflection elements 80 promote the removal of a pasty substance enteringthe cylindrical housing section 44 via the inlet openings 68,70. Thispromoted and thus intensified removal of the pasty substances in axialdirection reduces the danger of contamination of the two pastysubstances, i.e. the undesired mixing of the two pasty substances ortheir contamination in the direction of the inlet openings 68,70 intothe ducts 64,66 and possibly up to the outlet stubs 28,30. Ifcontamination and thus polymerization occurs in these areas, it is nolonger possible to discharge any residual material of the bags 20,22owing to clogged outlet stubs 28,30.

Another feature of the dynamic mixer 36 is to be explained withreference to FIG. 6. The mixer elements 74 described above are of rigidconfiguration and essentially radially protruding webs which causeswirling of the substance flows due to rotation of the axis 72. Inaddition to the rigid mixer elements 74 the dynamic mixer 36 comprisesfurther mixer elements 84 designed as thin and flexible webs, said mixerelements 84 moving from the inside along the inner side 76 of thecylindrical housing section 44. These additional flexible mixer elements84, too, cause swirling of the substance flows. One flexible mixerelement 84 per plane is provided in a plurality of contiguous radialplanes of the mixer shaft 38, said mixer elements 84 being staggeredfrom radial plane to radial plane by a constant angular range. The sameapplies to the mixer elements 78 and 78′, respectively, which connecttwo adjacent mixer elements 74 and are also staggered from radial planeto radial plane, in this case by 90°. Said mixer elements 84 and themixer elements 78 and 78′, respectively, are thus uniformly distributedalong a helical line about the axis 72. Both types of mixer elements arevery well suited for homogeneous mixing of pasty substances in a dynamicmixer 36 which can also be referred to as continuous mixer.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined the appended claims.

What is claimed is:
 1. A device for mixing two pasty substancescomprising housing (42) including a substantially tubular section (44),said substantially tubular section (44) having two inlet openings (68,70), each for receiving a pasty substance at a rear end (48) of thehousing (42) and an outlet opening (52) for discharging an admixed pastysubstance from a front end of the tubular section (44), a rotatablemixer shaft (38) extending into the tubular section (44) and beingrotatably supported in the housing (42), the mixer shaft (38) includinga plurality of rigid mixer elements (74) protruding from an axis (72)thereof for admixing the two pasty substances during their passagethrough the tubular section (44), an annular insertion part (62) withinthe rear end (48) of the housing (42) disposed substantially concentricto the axis (72), the insertion part (62) including an inner surfacefacing the tubular section (44) of the housing (42) and an outer surfaceforming the rear end (48) of the housing (42), said rear end (48) of thehousing (42) having two inlet stubs (54, 56), said mixer shaft (38)including a mixer shaft portion adjacent the inlet openings (68, 70)carrying at least one deflection element (80) for deflecting the pastysubstances fed through the inlet openings (68, 70) substantially axiallyinto the tubular section (44) of the housing (42), said at least onedeflection element (80) including a deflection surface (82) extendingabout the axis (72) and at an inclination to a radial plane thereof, theinsertion part (62) being provided with a cylindrical recess (69)housing said mixer shaft portion and the at least one deflection element(80), two ducts (64, 66) extending from said two inlet stubs (54, 56) tosaid inlet openings (68, 70), and said two ducts (64, 66) opensubstantially radially into said cylindrical recess (69).
 2. The mixingdevice as defined in claim 1 wherein the at least one deflection element(80) is of a wedge configuration.
 3. The mixing device as defined inclaim 2 wherein the at least one deflection element (80) is defined bytwo deflection elements (80, 80) disposed in diametrically oppositerelationship to each other and to the axis (72).
 4. The mixing device asdefined in claim 2 wherein the at least one deflection element (80) isdefined by two deflection elements (80, 80) extending over an angularrange of between 90° to 180°.
 5. The mixing device as defined in claim 4wherein said tubular section (44) includes an inner surface (76), and anidentical number of said mixer elements (74) lie as a group within eachof a plurality of radial planes of the axis (72) and extend contiguousto the inner surface (76) of the tubular section (74).
 6. The mixingdevice as defined in claim 2 wherein the at least one deflection element(80) includes a deflection surface (82) extending helically about theaxis (72).
 7. The mixing device as defined in claim 6 wherein saidtubular section (44) includes an inner surface (76), and an identicalnumber of said mixer elements (74) lie as a group within each of aplurality of radial planes of the axis (72) and extend contiguous to theinner surface (76) of the tubular section (74).
 8. The mixing device asdefined in claim 2 wherein said tubular section (44) includes an innersurface (76), and an identical number of said mixer elements (74) lie asa group within each of a plurality of radial planes of the axis (72) andextend contiguous to the inner surface (76) of the tubular section (74).9. The mixing device as defined in claim 1 wherein the at least onedeflection element (80) is defined by two deflection elements (80, 80)disposed in diametrically opposite relationship to each other and to theaxis (72).
 10. The mixing device as defined in claim 9 wherein the atleast one deflection element (80) is defined by two deflection elements(80, 80) extending over an angular range of between 90° to 180°.
 11. Themixing device as defined in claim 10 wherein said tubular section (44)includes an inner surface (76), and an identical number of said mixerelements (74) lie as a group within each of a plurality of radial planesof the axis (72) and extend contiguous to the inner surface (76) of thetubular section (74).
 12. The mixing device as defined in claim 9wherein the at least one deflection element (80) includes a deflectionsurface (82) extending helically about the axis (72).
 13. The mixingdevice as defined in claim 12 wherein said tubular section (44) includesan inner surface (76), and an identical number of said mixer elements(74) lie as a group within each of a plurality of radial planes of theaxis (72) and extend contiguous to the inner surface (76) of the tubularsection (74).
 14. The mixing device as defined in claim 9 wherein saidtubular section (44) includes an inner surface (76), and an identicalnumber of said mixer elements (74) lie as a group within each of aplurality of radial planes of the axis (72) and extend contiguous to theinner surface (76) of the tubular section (74).
 15. The mixing device asdefined in claim 1 wherein the at least one deflection element (80) isdefined by two deflection elements (80, 80) extending over an angularrange of between 90° to 180°.
 16. The mixing device as defined in claim15 wherein the at least one deflection element (80) includes adeflection surface (82) extending helically about the axis (72).
 17. Themixing device as defined in claim 16 wherein said tubular section (44)includes an inner surface (76), and an identical number of said mixerelements (74) lie as a group within each of a plurality of radial planesof the axis (72) and extend contiguous to the inner surface (76) of thetubular section (74).
 18. The mixing device as defined in claim 15wherein said tubular section (44) includes an inner surface (76), and anidentical number of said mixer elements (74) lie as a group within eachof a plurality of radial planes of the axis (72) and extend contiguousto the inner surface (76) of the tubular section (74).
 19. The mixingdevice as defined in claim 1 wherein the at least one deflection element(80) includes a deflection surface (82) extending helically about theaxis (72).
 20. The mixing device as defined in claim 19 wherein saidtubular section (44) includes an inner surface (76), and an identicalnumber of said mixer elements (74) lie as a group within each of aplurality of radial planes of the axis (72) and extend contiguous to theinner surface (76) of the tubular section (74).
 21. The mixing device asdefined in claim 1 wherein said tubular section (44) includes an innersurface (76), and an identical number of said mixer elements (74) lie asa group within each of a plurality of radial planes of the axis (72) andextend contiguous to the inner surface (76) of the tubular section (74).22. The mixing device as defined in claim 21 wherein at least two mixerelements (74, 74) in the same radial plane are connected to each otherby a circumferential portion (78, 78′).